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Once a broken bone is diagnosed, we typically splint rather than cast because splints allow the injured limb to swell.

Placing the limb in a cast immediately, on the other hand, sets up the potential for reduced circulation. In other words, it’s essentially applying a plaster tourniquet to an injured arm or leg.

Once the splint is applied, the patient is referred to an orthopedic specialist who probably will apply a cast once the swelling has decreased, usually in a few days.

This is when life gets tricky for us. Casts are vexing to emergency physicians. Whenever a patient expresses concern about a cast, I need to figure out whether it has anything to do with their problem.

Most commonly, patients come to the emergency department with concerns about the cast itself. It’s too tight. It’s too loose. What is this stuff draining from it? Why are my fingers or toes tingling?

All of these are valid concerns and can frequently be evaluated only by removing the cast to examine the arm or leg.

We do this by sawing through the cast on each side and opening it like a clamshell. This allows us to look at the skin and make sure that there is no sign of blisters from ill-placed padding and no infection.

Removing the cast allows us to complete a detailed vascular and neurological exam and make sure the cast isn’t too tight.It also allows us to assess swelling and rule out serious complications that can occur if there is too much swelling.

A complication from swelling is called “compartment syndrome” and is most common in the lower leg. It can result in permanent damage to nerves and blood vessels if not recognized and treated with surgery.

Life-threatening complications associated with casts, such as deep venous thrombosis, are even more daunting.

My most-memorable case involved a 35-year-old woman brought in by paramedics after she complained at home of chest pain and difficulty breathing.

The symptoms had occurred suddenly while she was resting at home after breaking her tibia and fibula — the two major bones between the knee and ankle — in a car crash the week before.

Her shortness of breath was so severe that her family immediately called 911. By the time paramedics arrived, they noted that her oxygen level was dangerously low and her blood pressure was dropping fast.

By the time she reached the emergency department, she had stopped breathing, and her pulse was lost. Paramedics flew in the doors having just started CPR.

The cast on her leg was the biggest clue to what had caused her cardiac arrest: a blood clot.

The cast hid the physical signs we look for, including an engorged vein. The clot had become unstable and had broken off and traveled to her lungs.

There, the clot starved her lungs of blood flow and subsequently starved her brain and heart of oxygen.